Electron Configuration

Page 6

Steps to Write Electron Configuration

  1. Identify how many electrons are in the atom.

Example: Carbon has 6 electrons

  1. Determine the principal energy level (n) of the atom
n = 2 for carbon (it is in the second period)
  1. Determine the number of sublevels.

· In principal energy level 1, there is 1 (1s).

· In principal energy level 2, there are 4 (2s, 2p, 2p, 2p)

· So for carbon we are working with 5 potential sublevels (they might not all be used).

  1. Assign electrons to the sublevels following the three rules (Aufbau, Pauli Exclusion, and Hund’s).

· 1s will be filled first, with the maximum of 2 electrons. You still have four electrons left.

· 2s will be filled next, with the maximum of 2 electrons. You still have two electrons left.

· 2p will be filled next, with the maximum of 2 electrons. You don’t have any electrons left now.

Steps to Draw and Orbital Notation

  1. Lowest energy to Higher energy
  2. When you add electrons the energy of the orbital can change.
  3. Orbital notation refers to the electron configuration of an element.
The orbitals can also only hold a certain number and the limits are as follows:

s=2

p=6

d=10

f=14
4. The notation tells you how many electrons are in the element, what orbitals of the atom they are in, and in what direction the electrons are spinning.


The Pauli Exclusion Principle-
No two electrons in an atom can have the same set of four quantum numbers.

Hunds Rule-The most stable arrangement of electrons is one with the maximum number of unpaired electrons. It minimizes electron-electron repulsions

and stabilizes the atom.

Steps How to Write Orbital Notation:

1) Fill in going horizontally to the right across the table. the s sublevels are first, then p, d, and then f.

2) s orbitals carry 2 electrons, p orbitals carry 6, d 10, and f 14.

3) Put the numbers in as you move along, until you reach the element you desire. Another thing is that there are a few exceptions.

Mg = [Ne] 3s2

Use the noble gas configuration for short handed notation. Long handed is just the electron config. of neon plus the valence electrons for Mg.


1s2 2s2 2p6 3s2

As a semi-check, you can add the electrons together to reach the atomic number. In this case, adding 2+2+6+2 = 12, the atomic number of Mg.
How to Write the Orbital Notation for Iron - Mr. Causey's Chemistry